Do you have more details on this? For example, where did you define the MSL class for the PCBs? A screenshot would certainly help 

Hello Mike, 

Thanks for the feedback. My question was exactly where is it defined. My colleague finally found that the MSL class is in Part. So now I know how to proceed. Thanks a lot. 

Okay. But this is either a customisation or a field from a special IFS module. Because it does not exist in the standard: 

But at least your question has been clarified